Best of both?

[dawson]

Sorry for starting yet another new thread!

 

All this talk of Barlow lenses, focal length, focal ratio, DSOs, planets etc has got me thinking... Always dangerous.

 

Fast scopes (low f/ numbers) with wide field of views are best for imaging DSOs. Slow scopes (high f/ numbers) with narrower field of views are for planetary and lunar stuff.

 

So, to get the best of both worlds:

 

1. Get a fast scope for the DSO stuff, and use secondary optics (Barlow, powermate etc) to slow it down for planetary.

 

2. Get a slower scope for the solar system stuff, and use secondary optics (focal reducer etc) to speed it up for DSO.

 

Which method would give the best results for both circumstances?

 

I suspect it is easier to slow a fast scope down, than try and open up the FOV in a slower scope.

 

I'd be interested to see what impact a focal reducer would have on my F/11.8 scope. Maybe if someone has one we can try that at a meet sometime.

 

James

 

[Guest Ely Ellis]

I would think buy a fast scope and slow it down by reducing the aperture.

ie. Put the lens cap on and open up the small cap, if you have one.

There's probably more to it than that though as it sounds too easy!

[T A WOW]

I would imagine slowing down a fast scope would be easier as you can just use a Barlow/powermate, and that will work on any scope/set up. Speeding up a scope is still possible but (as far as I'm aware) you can only achieve this with focal reducers, which are usually specific to a particular scope and often fairly expensive.

As for just putting the lens cap on I personally wouldn't imagine that would work, my reasoning being that you still get the same mag with any EP with the cap on or off. (of course I may be completely wrong)

Edit: putting the lens cap on would only change the F/ratio not the F/length so EP mag would not change.

Edited March 17, 2013 by T A WOW

[Brantuk]

It's hard to find one scope that fits all situations. An Sct is the nearest you'll get imho - you can get them down to about f-6. But if you want a pure dso imaging scope and good planetary imaging scope then you'll almost have to buy two ota's. The secret is to have a good mount that will take them both for either imaging or observing.

 

That's what most folks do as far as I've seen. Start with the mount - an NEQ6 Pro will do all you want  or HEQ5 Pro to a slightly lesser degree - then select your scopes.